The primary driver for the development of renewable energy strategies is current concern over the potential, irreversible environmental damage that may occur with the continued or accelerated use of fossil fuels. In addition, the presently usable supply of fossil fuels is limited. Roughly 25% of all natural gas reserves are contaminated by carbon dioxide (CO2) and cannot be economically developed for use in existing pipeline systems. Hydrogen sulfide (H2S) is also a common component of natural gas, and it is highly toxic and corrosive to pipelines and gas processing equipment.
Movement toward a hydrogen based economy is an essential aspect of the United States' program to address the concern over environmental damage, as well as concerns over pollution in cities and associated health costs. However, current methods for producing hydrogen incur a large environmental liability, because fossil fuels are burned to supply the energy to reform natural gas (primarily methane, CH4) to produce hydrogen (H2).
High temperatures are required for producing hydrogen and synthesis gas, a combination of carbon monoxide (CO) and H2, from carbon-containing reactants. For example, H2 is produced at high purity by the direct thermal dissociation of methane.CH4+Heat→C+2H2  (1)at temperatures above approximately 1500° K. H2 can also be produced by the direct thermal dissociation of H2S.H2S+Heat→H2+S  (2)Synthesis gas can also be produced by the “dry reforming” of methaneCO2+CH4+heat→2CO+2 H2  (3)or the carbon reduction of waterC+H2O+heat→CO+H2.  (4)Reaction (3) has the added benefit of potentially using sequestered CO2 to produce synthesis gas. Thus, an opportunity exists for using natural gas containing relatively high concentrations of CO2 and H2S as a precursor to synthesis gas.
Reactions (1-4) are typically not carried out separately in industry because the high temperatures require substantial energy input. Rather, they are usually coupled with fuel combustion reactions used to provide the required energy. For example, Matovich et al. (U.S. Pat. No. 4,095,974) describes an electrically heated high temperature aerosol reactor and process for carrying out reaction (1). However, the Matovich et al. process and others rely on conventional sources of heat and undesirable greenhouse gases that contribute to global warming, such as CO2, that are ultimately produced at the power plant or directly in the combustion zone of the reaction tube.
Matovich et al. includes results from a pilot plant scale demonstration that CH4 can be completely dissociated using a short residence time (fractions of a second to seconds) electrically heated aerosol flow reactor for temperatures greater than 2088° K. However, at a larger scale, the process is uneconomical and contributes to global warming due to high electricity costs and the generation of CO2 via the burning of carbonaceous fuels to produce the electricity.
Hence, there is a need to develop environmentally benign processes for the production of H2 or synthesis gas to be used as a “clean fuel” or as a precursor to chemicals, respectively. There is also a need to utilize known natural gas reserves containing high concentrations of CO2.